The present invention relates to a high stability vertical deflection circuit for a CRT display device.
In general, a conventional vertical deflection circuit is composed of a ramp wave signal generator, an amplifier having a negative feedback circuit and a deflection coil. In such vertical deflection circuit, amplitude of ramp signal generated by the ramp wave signal generator depends upon capacitance of an integrating capacitor thereof, resistance of a current limiting resistor and a source voltage, etc. When a amplitude of the ramp wave signal output of the generator varies with variation of ambient temperature, the vertical size of a display image on a display plane varies. Temperature dependency thereof is in the order of .+-.500 ppm/.degree.C. Therefore, with an ambient temperature variation of, for example, 20.degree. C. results in a variation of vertcal size of display image of about .+-.1%.
Such small vertical size variation of about .+-.1% may be negligible for an ordinary display. However, for an application in which high precision of display is required, it is necessary to restrict such variation within .+-.0.1%, which is difficult to realize according to the current level of the art.
Similarly, stability of vertical deviation of image is also difficult to obtain for such application.
An object of the present invention is to overcome the above mentioned difficulties.
Another object of the present invention is to provide a high stability vertical deflection circuit by which variations of vertical size and vertical position of a display image, that is, variation of deflection distortion, is minimized.